Spinocerebellar ataxia type 10 (SCA 10) is an autosomal dominant disease characterized by cerebellar ataxia, seizure and anticipation. The SCA1O mutation is a massive (4-22 kb) expansion of the ATTCT pentanucleotide repeat in intron 9 of E46, a novel gene of unknown function, on chromosome 22q13.3. The long-term objective of this project is to elucidate the molecular mechanisms of SCA1 0, and to develop rational treatment strategies based on the disease-causing mechanism for this progressive debilitating disease. This application will investigate the mechanism by which the expanded ATTCT repeat leads to the disease phenotype. The hypothesis of the proposed project is that an expansion of the ATTCT repeat causes the disease by altering the E46 transcript through a repeat size-dependent mechanism. SCA1 0 is one of the newly recognized dominantly inherited ataxias, and its epidemiological, clinical and genetic features have not been fully characterized. Thus, further characterization of the genotype, phenotype, and genotype-phenotype correlation in SCA10 patients needs to be the starting point of this project, and is designated as Specific Aim 1. Accomplishing this Specific Aim should strengthen our hypothesis that the disease-causing mechanism is dependent on the repeat size. Specific Aim 2 will examine the E46 transcripts in available tissues to look for quantitative changes, aberrantly processed transcripts and abnormal localization of transcripts in SCA10. Specific Aim 3 will investigate E46 protein functions by analyzing the quantities and isoforms of this protein by western blot, determining the protein localization by immuno-cytochemistry, isolating proteins that interact with the normal and, if detected, aberrant E46 protein products by yeast-two-hybrid and co-immunoprecipitation techniques, and developing E46-deficient cell culture models for cell survival, proliferation and differentiation studies. Data obtained from Specific Aims 2 and 3 will be compared with the expanded repeat size, when applicable. Accomplishing these Specific Aims will provide important insights into understanding the pathogenic consequences of this novel pentanucleotide expansion in SCA10.